In this project, optical spectroscopy and electron spin resonance are used to study the quantum structure of porphyrin compounds. High spectral resolution is obtained by the use of low temperatures and crystal host materials. The spectra from inequivalent porphyrin guest sites are separately recorded by narrow line laser excitation of fluorescence. Of particular interest in this project are the effects of impurity ligands on the spectra of porphyrins. A theoretical effort will be directed toward the calculation of the intensities of vibronic transitions. This is to facilitate the interpretation of the vibronic spectra of porphyrins, and particularly the changes in these spectra which occur when the porphyrins are in the presense of impurity ligands.